Flexible sealed plastic bags containing a product, such as foodstuffs, are in widespread usage. These flexible sealed plastic bags contain a gas which is placed in the package to maintain the integrity of the product during storage conditions. Furthermore, the flexible sealed bags must keep the foodstuffs from leaking from the bags. In bags containing foodstuffs, leakage of air into the package permits oxygen to contact the product which produces undesirable oxidation of the product lessening its shelf life. As a result, sealed plastic bags containing foodstuffs, such as potato chips, are inspected for seal defects in the bags, as well as small leaks in the face of the bags. The inspection process is still largely manual in nature. While manual inspection is quite satisfactory for locating defective bags, it has the disadvantage of being time consuming and costly given the labor which is involved.
The most common types of leaks in flexible packages are in the end seals. Often particulate matter, such as food particles, becomes caught on the surface where the end seal is to be made. As a result, when the end seals are being formed, a complete seal cannot be formed because the particulate matter bridges the opposing faces which are to be joined or the seal has insufficient strength because very little surface area of the opposing faces in the vicinity of the seals is actually joined.
Currently, there is a trend in the food industry to use automatic case packing machines which take product after it has been sealed in flexible plastic bags and place it automatically into cases, such as cardboard boxes, without manual intervention. Case packing machines placing product contained in flexible plastic bags operate properly when the product is stacked in a packing configuration. The packing configuration of the stacked bags should fall within a predetermined minimum and maximum height in order for the case packing machine to properly operate.
Furthermore, tests are used in the packing industry to test a whole case of packed product contained in flexible packages to detect so-called "microleaks" in the face of the package. This process is usually performed by manual submersion of the product into water to detect for the presence of bubbles being expelled out of the package when the package is pressurized by the person submerging the package. If any "microleaks" are found, the whole case of flexible packages is rejected which is indicative of the packaging material being used in a packaging line having a fault which requires the shut-down of the automatic packing line.
Certain automated devices have been developed for checking the integrity of seals on plastic bags which are packaged in an automatic packaging line. U.S. Pat. No. 4,649,740 discloses an apparatus and method for testing leaks in packages. The device disclosed in the '740 patent has a series of measuring stations through which bags are moved during the testing process. A group of probes are lowered into contact with the inflated bags at each of the series of stations. An encoding mechanism determines if at successive stations the contacting of the packages with the probes causes a significant decrease in the height of the package which is indicative of a faulty package. The device of the '740 patent does not check if the bags fall within a height tolerance between a minimum and a maximum height. U.S. Pat. No. 4,697,452 discloses an apparatus for testing the integrity of sealed packages. The device disclosed in the '452 patent checks to determine if a bag leaks under application of pressure applied by a movable arm or a fixed shoe. The apparatus of the '452 patent does not check for the bags being within a height tolerance between a minimum and a maximum height. U.S. Pat. No. 4,955,226 discloses a method and apparatus for automatically detecting the presence of holes in sealed plastic bags. The apparatus of the '226 patent initially loads the bag with a first movable member which moves downwardly into contact with the bag to expand the bag. Thereafter, a movable plate is lowered into contact with the bag while the bag is still under pressure from the first movable member. A displacement transducer contacts the bags which has a pair of tips which are displaced vertically upward in response to the lowering of the plate in contact with the bag. The sensed upward movement of the transducer tips is compared with the response which is produced by a bag without leaks to determine if seal integrity is present. The device of the '226 patent does not check if the bags fall within a height tolerance between a minimum and a maximum height. The device of the '226 patent is not designed to detect pinhole leaks which are leaks which are so small that an appreciably measurable amount of air cannot be measured from coming out of the bags in response to the lowering of the load device.
A significant need exists today for a device which permits the in-line testing of flexible package integrity and height at high throughputs such as 60 bags per minute which are typical of the throughput of automatic packaging lines for flexible packages containing a wide range of substances.
Furthermore, the usage of sealed, flexible plastic bags is becoming much more widespread than their long-standing use in the food industry. For example, water-soluble pouches are now used to package fertilizer and pesticides. The water-soluble pouch is packed within another plastic bag which is ripped open when it is desired to use the fertilizer or pesticide. These packages contain hazardous materials which are not intended to contact the user who is opening the packages to place the inner water-soluble bag into liquid to dissolve it. Additionally, other types of sealed plastic bags containing fluids, such as IV bags and disposable contact lenses, are becoming more widespread in use which also must be tested for seal integrity desirably at a high throughput rate achieved during an in-line packaging process.
Furthermore, a need exists for a device which automatically checks, as part of an automated packaging process, seal integrity of flexible plastic packages as well as determining if the flexible packages fall within acceptable height specifications to facilitate the use of automatic case packaging machines. The checking of flexible packages for leaks and height tolerance at a single testing station in-line with a packaging process would permit a higher production throughput to be achieved as well as insuring high quality packaging at reduced cost.